(i) Field of the Invention
The present invention relates to blow bottles of a polyolefin resin. More specifically, it relates to blow bottles of a polyolefin resin which are extremely excellent in transparency and free from odor and which have good moldability.
(ii) Description of the Related Art
Polypropylene blow bottles are excellent in properties such as stiffness, impact resistance and chemical resistance, but on the contrary, they have drawbacks such as poor transparency and restriction on applications.
Japanese Patent Application Laid-open No. 60-124643 discloses a blend of a high-density polyethylene (HDPE) and a straight-chain or linear low-density polyethylene (LLDPE) and containers prepared therefrom, and Japanese Patent Application Laid-open No. 63-162740 discloses an olefin resin composition for injection blow molding which comprises a specific polypropylene and a polyethylene. Furthermore, for the purpose of improving transparency, Japanese Patent Application Laid-open No. 3-14852 discloses blow molded containers of a propylene polymer composition containing 3-methylbutene-1, and Japanese Patent Application Laid-open No. 60-127336 discloses blow molded transparent containers prepared from a polypropylene using a nucleating agent.
The employment of the nucleating agent leads to drawbacks such as high crystallization rate, narrow molding conditions and poor productivity. Most of the nucleating agents give off extremely unpleasant odor, and particularly in the fields of medicines and foods, the problem of odor is the largest fault. In consequence, the employment of the odorous nucleating agent cannot provide practical blow bottles.
In addition, for the purpose of improving the appearance of containers and injection blow moldability, a method for randomly copolymerizing propylene of the main component with ethylene is employed, but in this case, the transparency of the obtained containers unexpectedly begins to deteriorate from a certain point, as the proportion of ethylene to be copolymerized increases. Therefore, in the case of a crystalline ethylene-propylene random copolymer, the ethylene content for maintaining transparency is limited to the range of 7 to 10% by weight, which is not always sufficient to improve the blow molded containers to a satisfactory degree.
Moreover, also with regard to a composition containing 3-methylbutene-1 disclosed in Japanese Patent Application Laid-open No. 3-14852, the transparency cannot be improved to a satisfactory degree, and the tolerance range of molding conditions is limited and productivity is also poor. Particularly, in the case of molded articles such as blow or blown articles for which a cooling effect is poor, it is difficult to heighten the transparency.